Vehicle stability control method

Abstract

A method of controlling travel of a vehicle equipped with an antilock braking system, including the steps of determining potential for one or more wheels to lift off the ground, deactivating the system in respect of the wheels with the lift off potential so the speed of these wheels is not taken into consideration when determining if anti-lock braking is required, applying a low-level test braking force to one or more of the wheels that has the lift off potential, monitoring the speed of the one or more wheels, and if the test braking force causes the wheel speed to fall below a predetermined percentage of the vehicle speed, triggering a stability alarm signal and/or applying a controlled braking force to reduce the vehicle speed.

What is claimed is: 
     
       1. A method of controlling travel of a vehicle equipped with an antilock braking system, the method comprising the steps of:
 determining a potential for one or more wheels of the vehicle to lift off the ground; 
 deactivating the anti-lock braking system in respect of the wheels with the potential to lift off the ground so that the speed of these wheels is not taken into consideration when determining to apply anti-lock braking control; 
 applying a low-level test braking force to the wheels with the potential to lift off the ground; 
 monitoring the speed of the wheels with the potential to lift off the ground; 
 triggering a stability alarm signal and/or initiating a control intervention to reduce the vehicle speed when the test braking force causes the speed of the wheels with the potential to lift off the ground falls below a predetermined percentage of the vehicle speed; and 
 increasing the braking force applied to the wheels without potential to lift off the ground by a greater amount than the braking force applied to the wheels with potential to lift off the ground when it is determined that there is potential for one or more of the wheels to lift off the ground during braking following braking demand from a driver of the vehicle, or when the driver issues a demand for braking during a braking test pulse, where the braking demand requires a braking force which is below a predetermined level. 
 
     
     
       2. The method of  claim 1 , wherein the step of initiating a control intervention includes applying a controlled braking force to one or more of the wheels which do not have potential to lift off the ground so as to reduce the vehicle speed. 
     
     
       3. The method of  claim 1 , further comprising monitoring the potential for one or more of the vehicle wheels to lift off the ground, and ceasing the control intervention when the potential for one or more of the vehicle wheels to lift off the ground is no longer present. 
     
     
       4. The method of  claim 1 , further comprising applying further low level test braking pulses to the wheel or wheels which has the potential to lift off the ground, monitoring the speed of the or each of the said wheels, and ceasing the control intervention when the speed of the or each of the monitored wheels does not change significantly relatively to the speed of the vehicle following the application of the test braking pulse. 
     
     
       5. The method of  claim 1 , wherein determining the potential for one or more of the vehicle wheels to lift off the ground includes measuring the lateral acceleration of the vehicle. 
     
     
       6. A vehicle braking system comprising:
 an electronic control unit of an electronic braking system including antilock braking control, the control unit being operable to provide a braking signal to a plurality of brake actuators associated with wheels on first and second sides of the vehicle, the control unit having the capability of determining a potential for one or more wheels of the vehicle to lift off the ground, wherein the control unit performs a method according to the following steps:
 deactivating the anti-lock braking system in respect of the wheels with the potential to lift off the ground so that the speed of these wheels is not taken into consideration when determining to apply anti-lock braking control, 
 generating a braking signal to apply a low-level test braking force to the wheel or one of the wheels that has the potential to lift off the ground, 
 monitoring the speed of the said wheel or wheels, and 
 triggering a stability alarm signal and/or initiating a control intervention to reduce the vehicle speed when the test braking force causes the speed of the or one or more of the monitored wheels to fall below a predetermined percentage of the vehicle speed, and 
 
 increasing the braking force applied to the wheels without potential to lift off the ground by a greater amount than the braking force applied to the wheels with potential to lift off the ground when it is determined that there is potential for one or more of the wheels to lift of the ground during braking following braking demand from a driver of the vehicle, or when the driver issues a demand for braking during a braking test pulse, where the braking demand requires a braking force which is below a predetermined level.